Spark plug and method of making the same



Sept. 8, 1936. J, A, JEFFERY SPARK PLUG AND METHOD OF MAKING THE SAME JOSEPH /7. JEFFER Y Patented Sept. 8, 1936 PATENT OFFICE SPARK PLUG AND METHOD OF MAKING THE SAME Joseph A. Jefl'ery, Detroit, Mich., assignor, by

mesne assignments, to

Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application June 24, 1931, Serial N6. 546,55: 9 Claims. ((1123-1653) This invention relates to an improvement in spark plugs.

The object'of the invention is to produce a spark plug which will have an insulating member, at least that .portion of which is exposed to the flame of an internal combustion engine being composed of a material which has high resistance to chemical reaction with hot gases generally found in the combustion chamber of an internal combustion engine; having high refractory qualities, high heat conductivity, high heat expansion and a high, hot dielectric, and being also dense and substantially impermeable to gases. A particular object is to guard against the deleterious results of the fluxing action on the glaze of usual spark plugs which is caused by lead compounds deposited on the plugs when ethyl gas is used.

The objects of the invention are obtained by making at least a portion of the spark plug, that is exposed to the flames of an internal combustion engine, from a composition consisting substantially of magnesimn oxid. Details of the invention will appear as the description proceeds.

In the drawing, Figure 1 represents a longitudinal section through one form of the improved spark plug where the insulating member is made in one piece; Fig. 2 is a similar longitudinal section through a plug where the exposed tip of the spark plug insulator is made from a different material from that composing the outer part of the insulator; Fig. 3 is a section similar to Fig. 2, but showing a diiferent form of joint between the two parts of the insulator; and Fig. i is a section similar to Fig. 1, but showing a two part core and a two part insulator.

The construction shown in Fig. 1 comprises an insulating member I which has extending there through an electrode ll. Surrounding the insulator there is the usual member l2 adapted to be screwed into a threaded opening in the cylinder 01' an internal combustion engine. The insulator body is provided with a shoulder l3, the lower side of which rests upon a packing l4 interposed between it and a shoulder l5 of casing l2. A threaded sleeve i6 screws into the upper end of member I! and compresses a packing l7 against the upper side of shoulder l3. Electrode l8 extends from the lower end of member I 2 to sparking relation with the lower end of electrode ll.

The construction above described is old so far as the shape and relation of the various parts is concerned, the novelty lying in the composition of the insulator III, which is substantially all magnesium oxid.

It is almost impossible to melt magnesium oxid so as to cast it with known appliances. It has been discovered, however, that granulated magnesium oxid, especially if the granules are of selected sizes so as to pack to the best possible advantage, can be pressed into shape and then sintered sufficiently to form a dense body substantially impermeable to gases and having all of the qualities enumerated above as desirable in the insulating member of a spark plug. It is preferable to form the body of graduated sizes 10 of granules and press it by the dry pressingmeth- 0d under high pressure, so as to pack the particles as densely and in as intimate relation as possible before the firing action. 7

It has been found that a very small amount of oxid of cobalt or chromium oxid, CrzOa, added to the magnesium oxid, reduces the necessary temperature for sintering materially, without injuring the qualities of the resultant body, and while still leaving the product exceedingly refractory so that no temperature to which it is subjected in an internal combustion engine is injurious thereto. About one-tenth of one per cent of cobalt oxid has been used, and as an alternative the same amount of chromium oxid, this small trace of either of these oxids being sumcient to lower the sintering temperature of the magnesium oxid to a material extent. Other basic oxides having a similar efiect may be used.

- A body made in the above described manner produces a close knit and strong body when fired in a Dressler kiln to cone H, but small pores still remain in the body so that it is somewhat permeable to gases. A very satisfactory and practically impermeable core has been formed by sintering the body, a temperature of at least 1650 C. being required.

Figure 2 discloses a spark plug core similar to that shown in Fig. 1 except that it is made in two parts.

In the insulator body shown in Fig. 2 there is a tip 20 formed of approximately pure magnesium oxid, as described above. The lower end of this part 20 is that portion of the insulator body exposed directly to the flame of the gases ignited by the spark of the plug and, therefore, it is subjected to the highest heat conditions.

The upper end 2| of the insulator body is not subjected to as high temperature'as the low-- er end 20, and therefore, may be made of a suitable porce ain or other material not having as high insulating qualities under extremely high temperatures as magnesium oxid possesses. The two parts 01 the insulator may be united by a suitable refractory bond 22, which should also have a fairlyhigh hot dielectric, to avoid the striking of the spark from the central electrode ll through this bond to the shell I2.

In Fig. 3 there is shown a core similar to that shown in Fig. 2 except that the upper end of portion 20 is roughly conical, with ridges 23 thereon, while the lower end of portion 21 is provided with a socket 24 having grooves 25 therein so that refractory bond 22 will securely unite the two parts. The conical arrangement of the joint is desirable where the bond is not as good an insulator as other portions of the core, since this arrangement lengthens the path through the bond. This arrangement also provides for holding the two parts of the core in accurate alinement, so that the central passages for the electrode remain in alinement.

The form shown in Fig. 4 is similar to that shown in Fig. 2, with minor differences. The shell etc., are the same as shown in Fig. 1, and are accordingly designated by the same numerals. The inner end 20 of the insulator is made of magnesium oxide and has in its upper end a socket 26 into which there fits an extension 21 from the lower end of the-upper part 2l of the insulator. downward through part 20, and has a head 29 fitting in the bottom of socket 26. The electrode may be secured in place at 30 by screw threads or a suitable bond or both- The upper portion 2| of the insulator has an electrode 3! extending downward therethrough and termimating in a head 32 adapted to rest upon head 29. Electrode 3l' may be held in place by a nut 33 on' its screw threaded upper end.

In this construction the two parts of the insulator carry their respective portions of the electrode, and so may be handled and replaced separately. They may be held together by shoulder l and collar N5 of the shell.

The described method of making theinsulator body renders it convenient where it is desired to make the entire body of magnesium oxid, and this is the preferred construction, although the magnesium oxid composition is particularly necessary only in the more exposed portion of the body.

It will be readily understood that the shape of the insulator body may be changed as desired for various reasons, and that, where a two part body is formed, the exposed part may be held in position by other means than those An electrode 28 projects magnesium oxid.

2. A spark plug comprising an insulating body having the portion at the sparking end of the plug composed of approximately pure sintered magnesium oxid substantially impermeable to ases.

3. A spark plug comprising a unitary self-sustaining insulator body made entirely of substantially pure magnesium oxid.

4. A spark plug comprising a self-sustaining insulating body composed of upwards of 99% magnesium oxid and less than 1% of impurities.

5. A spark plug comprising a self-sustaining insulating body composed of upwards of 99% magnesium oxid and less than 1% of impurities and sintered into a body substantially impermeable to gases.

6. A spark plug comprising a self-sustaining insulating body composed of upwards of 99% magnesium oxid anda trace of a refractory oxid which lowers the sintering temperature of magnesium oxid without materially affecting the insulating qualities thereof.

'7. A spark plug comprising .a self-sustaining insulating body composed of upwards of 99% of magnesium oxid and a fraction of 1% of cobalt oxid.

8. A spark plug comprising a self-sustaining insulating body composed of upwards of 99% of magnesium oxid and a fraction of 1% of chromium oxid. I i

9. A spark plug comprising an insulating core having a shoulder around its middle and a shell pressing against the two sides or the shoulder, the core being divided into two separable parts across the shoulder, so that the shell presses the two parts of the core against each other, 50 the inner part of the core being of magnesium oxide.

JOSEPH A. JEFFERY. 

